I want my photoswhen I open iphoto it says rebuilding thumbnails cachesand all I get is empty squares with a dotted line around themIf I click on one it will have an explanation mark in the middle where a photo should be

When opening iPhoto from the dock (iPhoto must not be running) press and hold the 'Option + Command' then open iPhoto by clicking in the dock for iPhoto. This is the box you will see if you did it right.

Try using Spotlight and look for jpeg files. When you find some use QuickLook to see if it is one of the missing.

Spotlight is that magnifying glass looking thing in the upper right corner of your screen, use the keyword JPEG, originals or perhaps a filename of a photo.

It will show you the path to where it is located, then hold down the option key and open iPhoto, create a new library and then from the drop-down menu select 'Add to Library', navigate to where you found the originals folder and select it to import all the photos into the new library.